A low-complexity PAPR reduction SLM scheme for STBC MIMO-OFDM systems based on constellation extension

( Guang Li ),( Tianyun Li ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.6

Multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) is widely applied in wireless communication by virtue of its excellent properties in data transmission rate and transmission accuracy. However, as a major drawback of MIMO-OFDM systems, the high peak-to-average power ratio (PAPR) complicates the design of the power amplifier at the receiver end. Some available PAPR reduction methods such as selective mapping (SLM) suffer from high computational complexity. In this paper, a low-complexity SLM method based on active constellation extension (ACE) and joint space-time selective mapping (AST-SLM) for reducing PAPR in Alamouti STBC MIMO-OFDM systems is proposed. In SLM scheme, two IFFT operations are required for obtaining each transmission sequence pair, and the selected phase vector is transmitted as side information(SI). However, in the proposed AST-SLM method, only a few IFFT operations are required for generating all the transmission sequence pairs. The complexity of AST-SLM is at least 86% less than SLM. In addition, the SI needed in AST-SLM is at least 92.1% less than SLM by using the presented blind detection scheme to estimate SI. We show, analytically and with simulations, that AST-SLM can achieve significant performance of PAPR reduction and close performance of bit error rate (BER) compared to SLM scheme.

Nonlinear Finite Element Analysis of Prestressed Concrete Containment Vessel under Severe Accident Loads

Song Jin,Zhongcheng Li,Tianyun Lan,Zhanfa Dong,Jinxin Gong 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

Prestressed concrete containment vessel act as a reliable leak tight barrier during the accident conditions. There is a growing demand to study nonlinear behavior of containment structure under severe accident loads in depth. This paper presents nonlinear finite element analysis of prsestressed concrete containment vessel under severe accident loads with consideration of material nonlinearity, penetrations, local reinforcement and temperature-dependent degradationcharacteristic of materials. To reflect the prestressing effects realistically, non-uniform distribution of effective prestressing along the tendon profile is explicitly considered and python scripts are developed to add the corresponding temperature drop value for each node of the prestressed tendons to ABAQUS input files automatically. Nonlinear finite element analysis for pressure only case and combined thermal and pressure case has been investigated in detail. Nonlinear finite element analysis results of the containment structure indicate that, thermal effects have negligible effect on pressure capacity of containment, considering the thermal effects, pressure capacity of containment decrease not more than 5% and margin of the containment still meets the requirements of not less than 2.5. The effect of temperature exhibit significantly influence on displacement response of containment structure, and the effect of temperature on the strain of liner and reinforcing steel is much greater than that on prestressed tendon. Thermal effects exhibit the greatest influence on nonlinear displacement response of the dome apex location and the least influence on the 33 m elevation.

Analysis of Cable under Dynamic Contact and Large Deformation

Bingjian Wang,Qingbin Li,Tianyun Liu,Weibing Peng 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.4

For simulating contact interactions and high displacement gradients between the cable and the saddle at the middle tower of tripletower suspension bridges, a cable element is developed by combining the absolute nodal coordinate formulation and the quasiconforming technique. New curvature strains are developed and elastic forces are explicitly formulated for the cable elements. Thereafter, it is compared to the original one to verify its locking remedies. The numerical solutions using the element are compared to analytical results and solutions by the original element. Compared to the original, the proposed element suppresses the highfrequency disturbances in the velocity and acceleration curves. Using the element, the contact and sliding behavior between the cable and the saddle is analyzed by employing parameters obtained experimentally. The saddle’s mechanical and frictional performance subjected to different friction coefficients and unbalanced cable forces is investigated. The proposed model exhibits excellent accuracy in the prediction of the sliding force and the contact status between the cable and the saddle.

Validity Analysis of Spray Model by Comparing Simulated with Measured Spray Liquid and Vapor Phase

( Zhe Sun ),( Xue Dong ),( Peng Yin ),( Tianyun Li ),( David L. S. Hung ),( Min Xu ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

Gasoline direct injection (GDI) Engine is proved to be a key technology to save energy and reduce emissions, which improves the overall engine performance. Spray injection affect the fuel-air mixing directly and computational fluid dynamics(CFD)software is utilized to model the macroscopic shape of the spray and the vapor mass. In this paper, the liquid and vapor phase of the spray of a one-hole injector was studied both experimentally and numerically. The structure and concentration distribution of the vapor phase of the spray, vapor mass and spray penetration were measured using laser induced exciplex fluorescence (LIEF) technique in a constant volume chamber. The simulations were performed by the CONVERGE software. Both the spray penetration and Sauter Mean Diameter (SMD) employed in the simulation were calibrated with the in-chamber measurements. The comparison of vapor concentration between the simulated results and the measured results acquired from the chamber suggest that the evaporation model of the single component fuel has significant influence on the simulated results. In addition, an analysis based on the present evaporation model has been made in this study. The results show that the 2-D plane and local line distributions of vapor concentration in simulation do not best match those from the experiments. It is found to get higher vapor concentration in the simulation model, suggesting that the relationship between vapor concentration and evaporation rate should be considered and further verified.

SUPPRESSED PROMPT ATOMIZATION OF FLASHBOILING SPRAY BY ELEVATING INJECTION PRESSURE

( Qinglin Xu ),( Min Xu ),( David L. S. Hung ),( Tianyun Li ),( Xue Dong ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

In a direct injection spark ignition (DISI) engine, the mixing time of the fuel with intake air in the cylinder is limited, thus quicker atomization and evaporation are desired. In general, there are two viable ways to promote these processes. One of them is by increasing the injection pressure, which has always been the key technology adopted by automobile manufacturers to improve the engine performance and meet the emission regulations. While high-pressure injection is already applied in most of the DISI engines, it has been reported that further increase of injection pressure is still beneficial on fuel efficiency and emissions reduction. In addition to this, flash-boiling is also regarded as an effective way to improve fuel atomization and evaporation with the potential to reduce fuel consumption and emissions. Existing research on flash-boiling spray mainly focuses on the multi-hole injector. Its plume-to-plume interaction phenomenon, as called “collapse”, has been thoroughly studied. Its benefits on atomization and evaporation have been proved. However, limited work has been done on the flash-boiling spray of a single-hole injector. Its breakup mechanism and movement behavior need to be further studied. Moreover, the study of high pressure gasoline spray beyond 35 MPa is also limited, especially at flash-boiling conditions. The effects of injection pressure on flash-boiling spray is still unrevealed. Therefore, the objective of this work is to study the influence of the superheat degree and injection pressure on the spray penetration and dispersion of a single-hole injector. Results show that in promoting dispersion and reducing penetration of the fuel, the effect of superheat degree was better than that of high injection pressure. In addition, increasing injection pressure of superheated fuel led to the increase in the tip penetration and decrease in the spray width while the injection pressure had opposite effects on subcooled fuel spray.